If you are interested in breeding emperor scorpions, you will need to tell males from females. Just a note: if you do intend to breed them, please think about how you will find homes for all the offspring!
It takes some practice to tell the difference between male and female scorpions. When sexing emperor scorpions, it is best to examine the pectines -- these are small comb-like appendages on the ventral abdomen (underside) of the scorpion.
The pectines (sometimes also called pectens) are thought to have a sensory function, primarily to vibrations. In males, these are larger and more prominent, although it may take some experience comparing males and females to use this as a reliable indicator.
There is an excellent photo here: Sexing Emperor Scorpions
Adult males also tend to be a bit smaller than females, but this is unreliable as a tool to differentiate males and females.